In the wake of bio-terrorism, anthrax has become a real concern for public. Anthrax is listed as a category A biological disease by the CDC. Inhalation of anthrax spores can result in death due to rapid fatal hemorrhage. Since anthrax aerosol is odorless, invisible and easily spread, the most effective way to protect people from infection is vaccination. Skin patch vaccination with replication-incompetent recombinant adenovirus which is genetically engineered to encode pathogen antigens is a non-invasive, effective, safe and economical technology for vaccination. Recently, Vaxin, Inc. has generated recombinant adenovirus encoding anthrax protective antigen (PA), which can be used for skin patch anthrax vaccination. An important issue for the induction of protective responses is the efficacy of skin patch vaccination, which is dependent on the development of immune responses. Dendritic cells (DC) in the skin play a major role in the induction of immune responses to vaccinated antigens. Cutaneous application of vaccines induces DC migration from the skin to the spleen and regional lymph node where DC present vaccine antigens to lymphocytes and induce immune responses. Our recent studies have demonstrated that Slit2, a soluble protein expressed in the skin, inhibits DC migration out of the skin. Application of a soluble receptor for Slit2, Robo, can increase DC migration and enhance immune responses to antigen stimulation on the skin. The hypothesis of this proposal is that application of soluble Robo can enhance the efficacy of skin patch antrax vaccination. This Phase I study will first investigate against anthrax. Second, the effect of recombinant adenovirus encoding the soluble Robo on the efficacy of the anthrax vaccine will be examined. Finally, the study will determine the mechanism by which Robo increases the efficacy of skin-patch anthrax vaccination. Both RoboN and the anthrax vaccine will be applied to the skin without needle injection, completion of the studies in this proposal will also provide a protocol for enhancing the skin-patch anthrax vaccination. Ultimately, this protocol may also be applied for skin-patch vaccines to other pathogens and tumor antigens.